Over the years in aircraft airconditioning installations, the designers of such systems have routinely relied upon, as a power source for the airconditioning units, compressed air bled from the aircraft's propulsion system. This bleed air, as it is termed, provided a convenient source of pneumatic power to drive the airconditioning compressors as well as other components within the airconditioning system.
It has been long recognized that this approach to powering the airconditioning unit was inefficient. The use of bleed air from the propulsion system compressor tends to significantly reduce fuel efficiency of the propulsion system. The skyrocketing cost of fuel has driven even those not normally obsessed with fuel economy, such as the military, to seek ways to economize while simultaneously improving aircraft performance.
One such area has involved helicopters where the drawing off of bleed air has always been recognized as deleterious to the helicopter's propulsion system total lift and rate of lift capacity.
In an aircraft environment such as that which involves a helicopter, the incorporation of the invention to be described hereinafter, results in dramatic improvements in total lift capacity, rate of lift and fuel efficiency.
A review of the prior art reveals that those expansion air cooling airconditioning systems that employ a turbomachine as part of the system, typically mount all of the turbomachine's impellers on a single shaft to rotate at the same speed. In this arrangement, fans, compressors and turbines that inherently operate optimally at different speeds are all driven at the same speed. With this type of arrangement, the designer of the turbomachine must attempt to design blade configuration for fans, compressors and turbines so that they will function at a speed that is not optimum for each impeller use. The presence on a single shaft of a number of different impeller units operating at a set or selected speed has given rise to vibration problems and an overall reduced efficiency of the turbomachines. This problem can be solved by employing a plurality of shafts independently mounted, which shafts carry impeller blades that can be rotated at different speeds. The principal drawback to this solution resides in the fact that the turbomachine housing for the independently mounted shafts must be larger in size and weight. Increased size and weight are an anathema to aircraft design which constantly seeks to reduce size and weight. Merely mounting impeller carrying shafts concentrically, one upon the other, with no thought as to overall efficiency does not optimize efficiency.
The Horst Schutze U.S. Pat. No. 3,877,246 is typical of the best prior art approach where expansion air cooling is provided and involves a bleed air driven airconditioning system for an aircraft. In FIG. 1, there is illustrated a multiple, independently mounted shaft arrangement, and in FIG. 2, a single shaft with four sets of impeller blades mounted thereon and finally in FIGS. 3 and 4, multiple, concentrically mounted shafts which have not been mounted in respect of each other for optimum efficiency.
Another system of expansion air cooling which involves a bootstrap aircycle system is shown in the Rannenberg U.S. Pat. No. 3,428,242. In this system, high pressure bleed air 2 is fed to a compressor 6 which in turn, passes the air through a heat exchanger 12 and then, through a turbine 18 where the air cools as it expands. The Rannenberg patent shows a fan 36, turbine 18 and a compressor 6 all mounted on a common shaft to rotate in unison at the same speed.
The invention, to be described hereinafter, overcomes the problems of vibration and inefficiency that arise in the patents referred to above; all in a manner that reduces overall turbomachine size and weight while simultaneously avoiding vibration problems and improving efficiency.